Walk-behind self-propelled snow removing machines of the type concerned are known as disclosed, for example, in Japanese Patent Publication (JP-A) No. 2000-54335. As shown in FIG. 27 hereof, the disclosed snow removing machine 220 includes an operating section 221 mounted to extend between left and right handlebars 222L and 222R. The operating section 221 comprises an operation board, which is provided with a throttle lever 223 for adjustably controlling the throttle opening of an engine 224, a direction-speed control lever 225 for adjustably setting a travel direction and a travel speed of a machine body 226, and a multifunction lever 227 for controlling roll and pivot of a snow removing unit 228 and on-off (engaging and disengaging) operation of left and right clutches (now shown) disposed between the engine 224 and left and right travel units 229L and 229R.
During snow removing operation, the load on the snow removing unit 228 may vary due, for example, to variations in the physical nature and properties of piled snow to be removed. For instance, when the load on the snow removing unit 228 increases, the revolving speed of the engine 224 and the travel speed of the machine body 226 are cause to drop. In this instance, a human operator may recognize an increase in the load on the snow removing unit 228 by sensing a decrease in the travel speed of the snow removing machine 220. To avoid undue drop in the travel speed, which may result in an inefficient snow removing operation, the human operator, upon sensing of a reduction in the travel speed, shifts the throttle lever 223 in a direction to increase the throttle opening of the engine 224 to thereby increase the engine revolving speed (engine power). Since shifting of the throttle lever depending on the sensitive ability of the human operator occurs frequently during the snow removing operation, the efficiency and finishing quality of the snow removing operation rely largely on the skill of the human operator.
According to improvements proposed heretofore, the revolving speed of the engine and the travel speed of the sow removing machine are controlled to vary with a change in the load on the snow removing unit. The proposed improvements are not fully satisfactory in terms of the operability and user-friendliness of the operating section as well as the efficiency of the snow removing operation. Typical examples of the prior improvements are disclosed in Japanese Utility Model Laid-open Publication (JP-U-A) No. 3-32617 and Japanese Patent Laid-open Publication (JP-A) No. 2005-42310.
Accordingly, an object of the present invention is to provide a walk-behind self-propelled snow removing machine, which is easy to use for all human operators irrespective of their skill levels, highly user-friendly, and capable of achieving a snow removing operation efficiently with good finishing quality.